Using SPI to interface custom audio DAC board

Discussion of developmental aspects of the MiSTer Project.
olekk77
Posts: 14
Joined: Thu Feb 04, 2021 2:12 pm
Been thanked: 1 time

Using SPI to interface custom audio DAC board

Unread post by olekk77 »

Hi guys!

I want to hook up my custom Amiga audio DAC to the MISTer, for now my board has a 10x2 parallel interface (Stereo), and one LED filter pin, and i am thinking about hacking my own local version of the SYS framework and the minimig core, to be able to output directly from minimig Paula to by PCB DACs... first... just to test it for a very first time in full featured mode.... Until now i have only run the card from my mini Cyclone II board with a USB interface, playing tracker mods from UADE, streaming over USB..... So, now, with the DE10 nano, for the first time i can serve the DAC board directly from a full Paula implementation, and the full minimig.
I'm itching like a kid to test it out!

However... this is NOT portable with regards to the std io boards. Soooooo.... i was thinking about making my own custom io board with dac chips and opamps on it.... this time the serial interfaced burr brown PCM61 chips...., BUT due to the fan in the center, i dunno if there is room enough on the board.... anyway, if i go this route, How does the switches on the DE10 work? How is it configured, ho many cfg slots are left? So that i guess it is a 4bit cfg code? So that i could add to the std framework, my config, so not as to break anything, compatiblity?

Anyway.... thinking a bit deeper... it may be best to let the io board be left alone as it is.... not design a new custom one.

Then.... i was thinking.... what i really only need, is a 5 bit interface to a new board... a bottom board, below the USB HUB..... a full fledged multi core sound card!

But where do i connect it??? I'm thinking about the SPI interface which is on the newer digital IO board...
BUT then.... that connection is reserved for the RTC??

Is that configurable with the switches on the DE10? Will it break compatibility if i run my soundcard over that SPI conection? Am going to hack the sys framework for that yet, but if i could multiplex in a switch between RTC and my soundcard on that SPI slot?.... how to configure that? The switches on the DE10?

I need, 5 or 6 pins for IO... CLK, CS, DAT_L, DAT_R, and LED_FLT, and possible a notch filter bypass to, as my thought is for an Amiga soundcard, but with the ability to bypass the notch filter too, as in 1200 sound. Also to be able to use this audio circuit with other cores without the Amiga filters....

So.... i'm settling on SPI... i think... but can i use the port that is reserved for the RTC?

Hmmm..... after a little further reading... looks like that SPI header connects to the ARM?....
Has to be bridged then.... yuck! slow-mo connection?

Maybe it would be better to just make a TOS link input DAC board with the burr brown dacs and an opamp, without the Amiga hard filters..... only implement an analouge hard filter at 20KHz or something, always on... i.e... then use HDL filters in the core or the sys framework instad.... Will be a more universal solution... but, what i really wanted to do was to let the LF347 opamp form the filters...
S0urceror
Posts: 23
Joined: Sat Nov 21, 2020 4:11 pm
Has thanked: 1 time
Been thanked: 8 times

Re: Using SPI to interface custom audio DAC board

Unread post by S0urceror »

Hi Olekk,

I am currently implementing SPI via UserIO for the MSX core. I found out that the standard IO boards only allow around 200khz SPI clocks. This is due to the 10k pull-ups and the fact that the port is configured to do zero and Z and not zero and one.

I am thinking about creating a different IO board that solves the former. The latter has to be fixed in the framework.

For joysticks this is all fine but for fast IO the UserIO is not suited.
Post Reply